The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but is free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
Magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (AP1) with a layer of antiferromagnetic material such as PtMn. While an antiferromagnetic (AFM) material such as PtMn does not in and of itself have a magnetization, when exchange coupled with a magnetic material, it can strongly pin the magnetization of the ferromagnetic layer.
The magnetic signals are written to the magnetic medium by a write head that includes an electrically conductive write coil that passes between first and second poles. The poles are joined at a back gap region and separated from one another by a write gap in a pole tip region near the ABS. When a current passes through the coil, a resulting magnetic flux in the magnetic yoke generated a fringing magnetic field that extends between the pole tips fringes out to write a magnetic signal onto an adjacent magnetic medium.
The configuration of the magnetic poles in the pole tip region of the write head is very important to the magnetic performance. For example, the pole tips must have sufficient area to avoid choking off the flow of magnetic flux to the pole tip or saturating the pole tips. Also, since the width of the pole tips defines the track width of the write head, at least one of the poles must have a width that is sufficiently narrow to define a desired narrow track width. A smaller track width means that more tracks of data can be written onto a given amount of disk space. The write element should also be constructed to prevent undesired, stray magnetic fields, such as those that can contribute to adjacent track writing. For example, fields that extend laterally from the sides of the pole tips rather than straight from one pole to the other can result in a signal bleeding to an adjacent track and can interfere with the signal of that adjacent track.
However, in many ways these needs conflict with one another. For example, forming a pole with a narrow track width makes it difficult to avoid choking off the flux and, therefore, reduces magnetic write field strength. In addition, making a write pole that defines a narrow track width and which has a strong magnetic write field can promote stray side fields which can cause adjacent track intereference.
Therefore, there is a strong felt need for a write head structure that can define a very narrow track width, with sufficiently strong field strength and with minimal side writing while also avoiding stray fields. Such a write head structure would also preferably be manufacturable and cost effective to produce.